Biocide for well stimulation and treatment fluids

ABSTRACT

A well stimulation and or treatment fluid that includes water, other additives, and a biocide consisting of 3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective to inhibit bacterial growth and minimize antagonistic reactions between the biocide and other additives. Also disclosed are well injection compositions, stimulations, squeezing, waterflood, packing, cement compositions, and methods for cementing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/779,509, filed on Jul. 18, 2007; which is acontinuation-in-part application that relates to and claims the benefitof priority to U.S. patent application Ser. No. 11/497,724, filed onAug. 22, 2006, all of which are incorporated herein by reference intheir entireties.

BACKGROUND

The present disclosure generally relates to biocides, and moreparticularly, to the use of 3,5-dimethyl-1,3,5-thiadiazinane-2-thione(Thione) in gas and oil field well stimulation and treatment fluids. Thedisclosure relates to various forms of Thione including, but not limitedto, non-emulsified 3,5-dimethyl-1,3,5-thiadiazinane-2-thione (CBThione), an emulsified 3,5-dimethyl-1,3,5-thiadiazinane-2-thione (WBThione), and a dry 3,5-dimethyl-1,3,5-thiadiazinane-2-thione.

After a well is drilled into a subterranean geological formation thatcontains oil, natural gas, and water, every effort is made to maximizethe production of the oil and/or gas. To increase the permeability andflow of the oil and/or gas to the surface, the drilled wells are oftensubjected to well stimulation. Well stimulation generally refers toseveral post drilling processes used to clean the wellbore, enlargechannels, and increase pore space in the interval to be injected thusmaking it possible for fluids to move more readily into the formation.In addition, typical reservoir enhancement processes such as waterfloodneed to utilize biocide as part of the waterflood package.

A typical well or field treatment process generally includes pumpingspecially engineered fluids at high pressure and rate into thesubterranean geological formation. The high-pressure fluid (usuallywater with some specialty high viscosity fluid additives) exceeds therock strength and opens a fracture in the formation, which can extendout into the geological formation for as much as several hundred feet.Certain commonly used fracturing treatments generally comprise a carrierfluid (usually water or brine) and a polymer, which is also commonlyreferred to as a friction reducer. Many well stimulation fluids willfurther comprise a proppant. Other compositions used as fracturingfluids include water with additives, viscoelastic surfactant gels,gelled oils, crosslinkers, oxygen scavengers, and the like.

The well treatment fluid can be prepared by blending the polymer with anaqueous solution (sometimes an oil-based or a multi-phase fluid isdesirable); often, the polymer is a solvatable polysaccharide. Thepurpose of the polymer is generally to increase the viscosity of thefracturing fluid that aids in the creation of a fracture; and to thickenthe aqueous solution so that solid particles of proppant can besuspended in the solution for delivery into the fracture.

The polymers used in well treatment fluids are subjected to anenvironment conducive to bacterial growth and oxidative degradation. Thegrowth of the bacteria on polymers used in such fluids can materiallyalter the physical characteristics of the fluids. For example, bacterialaction can degrade the polymer, leading to loss of viscosity andsubsequent ineffectiveness of the fluids. Fluids that are especiallysusceptible to bacterial degradation are those that containpolysaccharide and/or synthetic polymers such as polyacrylamides,polyglycosans, carboxyalkyl ethers, and the like. In addition tobacterial degradation, these polymers are susceptible to oxidativedegradation in the presence of free oxygen. The degradation can bedirectly caused by free oxygen or mediated by aerobic microorganisms.Thus, for example, polyacrylamides are known to degrade to smallermolecular fragments in the presence of free oxygen. Because of this,biocides and oxygen scavengers are frequently added to the welltreatment fluid to control bacterial growth and oxygen degradation,respectively. Desirably, the biocide is selected to have minimal or nointeraction with any of the components in the well stimulation fluid.For example, the biocide should not affect fluid viscosity to anysignificant extent and should not affect the performance of oxygenscavengers contained within the fluid. The oxygen scavengers aregenerally derived from bisulfite salts.

Other desirable properties for the biocide are (a) cost effectiveness,e.g., cost per liter, cost per square meter treated, and cost per year;(b) safety, e.g., personnel risk assessment (for instance, toxic gasesor physical contact), neutralization requirements, registration,discharge to environment, and persistence; (c) compatibility with systemfluids, e.g., solubility, partition coefficient, pH, presence ofhydrogen sulfide, temperature, hardness, presence of metal ions orsulfates, level of total dissolved solids; (d) compatibility with othertreatment chemicals, e.g., corrosion inhibitors, scale inhibitors,demulsiflers, water clarifiers, well stimulation chemicals, andpolymers; and (e) handling, e.g., corrosiveness to metals andelastomers, freeze point, thermal stability, and separation ofcomponents.

Current well stimulation fluids generally employ either glutaraldehyde(Glut) or tetra-kis-hydroxymethyl)-phosphonium sulfate (THPS) to controlbacterial contamination. Glutaraldehyde can be problematic because it ishazardous to handle and has environmental concerns. Moreover, it hasbeen observed that Glut can deleteriously affect the fluid viscosity ofthe well treatment fluid at elevated temperatures; temperatures that arecommonly observed during use of the well treatment fluid. This can beproblematic in fracturing applications since the higher maintained fluidviscosity down hole could hinder flow back. In addition, Glut has beenshown to negatively impact the behavior of the oxygen scavenger.

With regard to THPS, although it has been shown to perform better thanGlut with respect to interaction with the oxygen scavengers, THPS hasbeen found to interact with the polymer and limit viscosity developmentwhen added pre-inversion and post-inversion. That is, THPS has beenobserved to interact with the polymer during shear and significantlyreduce fluid viscosity.

Thus, there remains a need for a more versatile biocide for use in wellstimulation fluids that can effectively control bacterial contaminationand have minimal interaction with the polymer and/or oxygen scavenger.

BRIEF SUMMARY

Well injection compositions and methods of using such compositions arealso disclosed. In one embodiment, a well injection compositioncomprises: an injection fluid for removing a production fluid from asubterranean formation; and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth. In an embodiment, a method of recovering aproduction fluid from a subterranean formation comprises: displacing awell injection composition through a wellbore down to the subterraneanformation to force the production fluid from the subterranean formation,the well injection composition comprising an injection fluid and abiocide comprising 3,5-dimethyl-1,3,5-thiadiazinane-2-thione in anamount effective to inhibit bacterial growth.

Cement compositions and methods of using such compositions are furtherdisclosed. In one embodiment, a cement composition comprises: a cement;and a biocide comprising 3,5-dimethyl-1,3,5-thiadiazinane-2-thione in anamount effective to inhibit bacterial growth. In another embodiment, amethod of cementing comprises: injecting a cement composition into apermeable zone of a wellbore, the cement composition comprising a cementand a biocide comprising 3,5-dimethyl-1,3,5,-thiadiazinane-2-thione inan amount effective to inhibit bacterial growth; and allowing the cementcomposition to set.

The disclosure may be understood more readily by reference to thefollowing detailed description of the various features of the disclosureand the examples included therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures wherein the like elements are numberedalike:

FIG. 1 graphically illustrates post inversion viscosity in centipoise(cPs) as a function of time for polymer fluid samples containing varyingamounts of biocide relative to a control not containing the biocide;

FIG. 2 graphically illustrates pre-inversion viscosity as a function oftime for polymer fluid samples containing 500 parts per million ofbiocide relative to a control not containing the biocide;

FIG. 3 graphically illustrates pre-inversion viscosity as a function oftime for polymer fluid samples containing 1,000 parts per million ofbiocide relative to a control not containing the biocide;

FIG. 4 graphically illustrates a bar graph of post inversion viscosityas a function of time for polymer fluid samples heated at a temperatureof 180° F. for defined period of times containing 500 parts per millionof biocide relative to a control not containing the biocide;

FIG. 5 graphically illustrates oxygen reduction potential in millivoltsfor polymer samples containing 120 parts per kilion of sodiummetabisulfite buffered to a pH of 6.4 and having 500 parts per millionof biocide;

FIG. 6 graphically illustrates percent friction reduction as a functionof time for various biocides including3,5-dimethyl-1,3,5-thiadiazinane-2-thione in a friction loop apparatus;

DETAILED DESCRIPTION

The present disclosure is generally directed to the use of3,5-dimethyl-1,3,5-thiadiazinane-2-thione (also commonly referred to as“Thione”) as a biocide in gas and oil well stimulations. Surprisingly,relative to popular biocides currently used in well stimulation fluids,3,5-dimethyl-1,3,5-thiadiazinane-2-thione is much more versatile andprovides a reduced interference with friction reducers in the wellstimulation fluid, a reduced interference with oxygen scavengers, andhas minimal interaction with friction reducers at elevated temperaturesrelative to conventional biocides such as Glut or THPS. The3,5-dimethyl-1,3,5-thiadiazinane-2-thione biocide can be used in anaqueous solution (CB Thione) or can be added to the well treatment fluidas an emulsified fluid (WB Thione) or as a dry product.

The well treatment fluid generally comprises at least one polymer.Preferred classes of polymers are polysaccharides or synthesizedpolymers. Suitable polymers include, but are not intended to be limitedto, galactomannan polymers and derivatized galactomannan polymers;starch; xanthan gums; hydroxycelluloses; hydroxyalkyl celluloses;polyvinyl alcohol polymers (such as homopolymers of vinyl alcohol andcopolymers of vinyl alcohol and vinyl acetate); and polymers (such ashomopolymers, copolymers, and terpolymers) that are the product of apolymerization reaction comprising one or more monomers selected fromthe group consisting of vinyl pyrrolidone,2-acrylamido-2-methylpropanesulfonic acid, acrylic acid and acrylamide,methacrylic acid, styrene sulfonic acid, acrylamide and other monomerscurrently used for oil well treatment polymers, among others. Certainpolyvinyl alcohol polymers can be prepared by hydrolyzing vinyl acetatepolymers. Preferably the polymer is water-soluble. Specific examples ofpolymers that can be used include, but are not intended to be limited tohydrolyzed polyacrylamide, guar gum, hydroxypropyl guar gum,carboxymethyl guar gum, carboxymethylhydroxypropyl guar gum,hydroxyethyl cellulose, carboxymethylhydroxyethyl cellulose,hydroxypropyl cellulose, copolymers of acrylic acid and acrylamide,xanthan, starches, and mixtures thereof, among others.

The amount of 3,5-dimethyl-1,3,5-thiadiazinane-2-thione in the wellstimulation fluid will vary, generally depending on the polymeremployed, the conditions of the water and the extent of prior bacterialmanifestation, the time period of bacterial growth, the generalenvironment where the biocide will be used, and the like. Thus, it isnot possible to delineate a minimal amount, however, one skilled in theart will be able to determine the minimal amount with undueexperimentation. There is no maximum amount, although large excesses maynot be desirable for economic reasons.

The 3,5-dimethyl-1,3,5-thiadiazinane-2-thione can be added directly asan emulsification, solid, or solution to the fluid used to make the wellstimulation fluid, to a concentrated polymer solution, and/or may bemade on a slug dose basis. The present disclosure is not intended to belimited to a particular method for making the well stimulation fluid.

Examples of bacteria to which the3,5-dimethyl-1,3,5-thiadiazinane-2-thione is effective and are commonlyfound in oil and gas field fluids and waters include, but are notintended to be limited to, aerobic, anaerobic, and facultative bacteria,sulfur reducing bacteria, acid producing bacteria, and the like.Specific examples include, but are not limited to, pseudomonad species,bacillus species, enterobacter species, serratia species, clostridiaspecies, and the like. It should be noted that it is expected that theuse of 3,5-dimethyl-1,3,5-thiadiazinane-2-thione in the well stimulationfluid will be effective to inhibit algae and fungi formation at the samebiocidal concentrations for bacterial effectiveness.

Well stimulation and completion (treatment) fluid compositions of thepresent disclosure can further comprise other additives. Additives aregenerally included to enhance the stability of the fluid compositionitself to prevent breakdown caused by exposure to oxygen, temperaturechange, trace metals, constituents of water added to the fluidcomposition, and to prevent non-optimal crosslinking reaction kinetics.The choice of components used in fluid compositions is dictated to alarge extent by the properties of the hydrocarbon-bearing formation onwhich they are to be used. Such additives can be selected from the groupconsisting of water, oils, salts (including organic salts),crosslinkers, polymers, biocides, corrosion inhibitors and dissolvers,pH modifiers (e.g., acids and bases), breakers, metal chelators, metalcomplexors, antioxidants, wetting agents, polymer stabilizers, claystabilizers, scale inhibitors and dissolvers, wax inhibitors anddissolvers, asphaltene precipitation inhibitors, water flow inhibitors,fluid loss additives, chemical grouts, diverters, sand consolidationchemicals, proppants, permeability modifiers, viscoelastic fluids, gases(e.g., nitrogen and carbon dioxide), and foaming agents.

For well stimulation, the fluid containing the3,5-dimethyl-1,3,5-thiadiazinane-2-thione biocide can be injecteddirectly into the wellbore to react with and/or dissolve substancesaffecting permeability; injected into the wellbore and into theformation to react with and/or dissolve small portions of the formationto create alternative flowpaths; or injected into the wellbore and intothe formation at pressures effective to fracture the formation.

In an additional embodiment, the3,5-dimethyl-1,3,5-thiadiazinane-2-thione can be employed as a biocidein a well injection composition. The well injection composition cancomprise an injection fluid for removing a production fluid such as oilfrom a subterranean formation and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth. The injection fluid can be any fluid suitablefor forcing the production fluid out of the subterranean formation andinto a production wellbore where it can be recovered. For example, theinjection fluid can comprise an aqueous fluid such as fresh water orsalt water (i.e., water containing one or more salts dissolved therein),e.g., brine (i.e., saturated salt water) or seawater. The biocidedescribed previously in relation to well stimulation fluids isappropriate for this application as well.

The foregoing well injection composition can be used in a floodingoperation (e.g., secondary flooding as opposed to a primary recoveryoperation which relies on natural forces to move the fluid) to recover aproduction fluid, e.g., oil, from a subterranean formation. The floodingoperation entails displacing the well injection composition through aninjection well (or wells) down to the subterranean formation to force ordrive the production fluid from the subterranean formation to aproduction well (or wells). The flooding can be repeated to increase theamount of production fluid recovered from the reservoir. In subsequentflooding operations, the injection fluid can be replaced with a fluidthat is miscible or partially miscible with the oil being recovered.

The injection well can include a cement sheath or column arranged in theannulus of a wellbore, wherein the annulus is disposed between the wallof the wellbore and a conduit such as a casing running through thewellbore. Thus, the well injection composition can pass down through thecasing into the subterranean formation during flooding. The biocidepresent in the well injection composition can serve to reduce bacterialgrowth on the cement sheath and the conduit therein withoutsignificantly affecting the materials with which it comes in contact,including the components of the well injection composition.

In yet another embodiment, the 3,5-dimethyl-1,3,5-thiadiazinane-2-thionecan be employed as a biocide in a cement composition, particularly acement composition used for squeeze cementing. The cement compositioncan comprise a cement and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth. The cement can be, for example, hydrauliccement, which comprises calcium, aluminum, silicon, oxygen, and/orsulfur, and which sets and hardens by reaction with water. Examples ofsuitable hydraulic cements include but are not limited to Portlandcements, pozzolana cements, gypsum cements, high alumina contentcements, silica cements, high alkalinity cements, and combinationscomprising at least one of the foregoing cements. More specific examplesof cements are class A, C, G, and H Portland cements. The cementcomposition can be stored in dry form until it is desired to place it ina wellbore, making the cement composition particularly useful insub-zero condition. The cement composition can be combined with a fluidfor rendering it flowable when it is desired to pump it into a wellbore.The fluid can comprise, for example, fresh water, salt water such asbrine or seawater, or a combination comprising at least one of theforegoing types of water.

As deemed appropriate by one skilled in the art, additional additivesmay be included in the cement composition for improving or changing itsproperties. Examples of such additives include but are not limited toset retarders, fluid loss control additives, defoamers, dispersingagents, set accelerators, and formation conditioning agents. Theadditives can be pre-blended with the dry cement composition before theaddition of a fluid thereto. Alternatively, the additives can beintroduced to the cement composition concurrent with or after theaddition of a fluid thereto.

The foregoing cement composition can be utilized in a remedial cementingoperation such as squeeze cementing, which is performed after theprimary cementing operation. In squeeze cementing, the cementcomposition can be combined with an aqueous solution and then forcedunder pressure into permeable zones through which fluid can undesirablymigrate in the wellbore. Examples of such permeable zones includefissures, cracks, fractures, streaks, flow channels, voids, highpermeability streaks, annular voids, and so forth. A permeable zone canbe present in the cement sheath residing in the annulu of the wellbore,in the wall of the conduit inside the cement sheath, and/or in amicroannulus between the cement sheath and the conduit. The transitiontime of the cement composition can be relatively short such that theamount of gas migration into the composition is limited. The cementcomposition is allowed to set within the permeable zone to form animpermeable mass that plugs the zone and prevents fluid from leakingtherethrough. The biocide present in the cement composition can serve toinhibit microbiological induced corrosion of the cement sheath and theconduit therein without significantly affecting the materials with whichit comes in contact, including the components of the cement composition.That is, the biocide can attack bacteria present on the cement sheathand the conduit to reduce the growth of the bacteria.

EXAMPLES

In the following examples, an in-house constructed Inversion Loop wasmodified with a Grace M3500 viscometer for periodically measuring fluidviscosity as a function of time. The ORP apparatus included a HACHsensION pH meter with a combination ORP electrode. In Example 7, afriction loop apparatus was employed

Example 1

In this example, the post inversion viscosity of a polymeric fluidhaving a biocide at different concentrations was analyzed relative to acontrol that did not include a biocide. The biocides analyzed included50% Glut, 35% THPS, 24% caustic based Thione (CB Thione), and a 20%water based Thione (WB Thione). A 0.1% aqueous stock solution ofpolyacrylamide-co-acrylic acid, was made and allowed to age for about 30minutes. For each of the samples tested, 1,500 grams of the stocksolution was first added to the inversion loop, recirculated, and theviscosity measured. After 2 minutes, the biocide was added at an initialconcentration of 250 parts per million (ppm) and allowed to recirculatefor 2 minutes at which time the viscosity was recorded. Additional 250ppm increments of the biocide were added and the viscosities measuredafter recirculation in the inversion loop for an additional 2 minutes.

The test results are graphically illustrated in FIG. 1. As shown,polymer shear is observed as a function of recirculation in theInversion Loop apparatus (see control). For post inversion, both Glutand WB Thione exhibited minimal effect on viscosity, even at the higherconcentrations. CB Thione, exhibited a slight reduction in polymerviscosity as a function of increasing concentration whereas asignificant viscosity reduction was observed with THPS.

Example 2

In this example, pre-inversion viscosity was measured for the variousbiocide/polymer fluids and control of Example 1, which were prepared inaccordance with Example 1. In those samples containing the biocide, thebiocide concentrations examined were 500 ppm and 1,000 ppm. The resultsare shown in FIGS. 2 and 3, respectively.

The results clearly show that THPS interacts with the polymer resultingin a significant decrease in viscosity. In contrast, the Glut and thesamples containing CB Thione and WB Thione showed minimal interactionrelative to the control sample. Interestingly, the WB Thione exhibitedan increase in viscosity relative to the control. While not wanting tobe bound by theory, the components used to form the emulsion arebelieved to react with or interact with the polymer.

Example 3

In this example, the effect of heat on the biocide/polymer fluids andcontrol of Example 1 was analyzed. THPS was not analyzed because of itsobserved interaction at room temperature in the earlier examples. Foreach of the samples that were tested, 500 ppm of the biocide was addedto 1,000 grams of the polyacrylamide stock solution of Example 1. Thesamples were added to the inversion loop, recirculated for 1 minute, andthe viscosity measured. The samples were then placed into an oven at180° F. for 4 hours, and were allowed to cool to room temperature (77°F.). Once the samples were at room temperature, the viscosity wasmeasured and then return to the oven for an additional 4 hours at whichthe time sample was cooled to room temperature and the viscositymeasured. The results are shown in FIG. 4.

From the results above, it can be noted that polymer viscosity degradeswith heat over time. For each test, the initial viscosity measurementshows only the effect of the biocide on the polymer viscosity. CB Thioneis the only one to give a significant reduction from that of the controlafter the first heating cycle, which was expected given the results seenin the previous post-inversion viscosity testing. After four hours attemperature, however, the viscosities of the control, CB Thione, and WBThione are essentially the same, while the viscosity of the Glut testsample has maintained nearly all its viscosity. This same effect is seenat the eight-hour mark, with the Glut sample showing only slightlyreduced viscosity. While not wanting to be bound by theory, it isbelieved that the glutaraldehyde slightly crosslinked the polymer atelevated temperature, thus allowing the polymer viscosity to persistabove that of the polymer alone. Reactions between dialdehyde andacrylamide are quite well documented. This effect could be consideredproblematic in fracturing applications since the higher maintainedviscosity down hole could potentially hinder flow back.

Example 4

In this example, the effect of CB Thione, WB Thione, THPS and Glut onthe oxygen scavenger was examined. To a beaker containing 500milliliters of deionized water, a 120 ppm dose of sodium metabisulfite(SMBS) was added and the pH and oxygen reduction potential (ORP) wererecorded. Once stabilized, phosphate buffer was added to increase the pHto 6.4 and the ORP recorded. Finally, the particular biocide tested wasadded at a concentration of 500 ppm. The ORP was recorded initially andafter a period of 10 minutes. The results are shown in FIG. 5.

From these results, it can be noted that there is a significantdifference in ORP response upon addition of each respective biocide. ORPis an indication of a solution's ability to oxidize or reduce anothersolution/species. Theoretically, the lower the ORP, the higher the ratioof reduced species to oxidized species. Glut does not significantlyimpact ORP upon initial addition, and after 10 minutes of residence timethe ORP actually increases nearly to the level of the DI H₂O alone. Thiswould indicate a negative impact on the bisulfite scavenger. Thereactions between aldehydes and bisulfite are well documented and areoften used for melting point determinations. Similar results wereobserved with THPS. In contrast, upon addition of the CB Thione, the ORPof the solution is lowered significantly. The lower value given by theCB Thione solution would indicate a more preferable environment for O₂scavenging to occur. WB Thione also indicated a more preferableenvironment for O₂ scavenging.

Example 5

In this example, a friction loop apparatus was employed to assess thecompatibility of biocide formulations with an anionic friction reducer.The biocides analyzed included 50% Glut, 35% THPS, 24% caustic basedThione (CB Thione), and a 20% water based Thione (WB Thione).

A commercial anionic friction reducing polymer was dosed at 0.5 gallonsper thousand gallons of water. The friction loop determined the effectof the polymer on the differential pressure across a 5 foot test sectionof 0.5″ nominal stainless steel pipe. The friction loop was operated ata flow rate of 24 gallons per minute, a temperature of about 85°Fahrenheit, and a Reynolds number of about 120,000. Differentialpressure was continually measured across the test section at one-secondintervals for a period of 10 minutes. The first minute of the test wasused to establish a baseline pressure drop. The friction reducer wasinjected into the system 1:00 minute after the test was started. Therespective biocides were injected into the system at a 500 ppm dosage3:00 minutes into the test, and an additional 500 ppm dosage wasinjected 5:00 minutes into the test.

The pressure drop data was used to calculate a percent frictionreduction in accordance with equation (1) below,

$\begin{matrix}{{{\% \mspace{14mu} {FR}} = \frac{{\Delta \; P_{solvent}} - {\Delta \; P_{solution}}}{\Delta \; P_{solvent}}},} & (1)\end{matrix}$

wherein % FR is the percent friction reduction, ΔP_(solvent) is thepressure drop across the test section for pure solvent (water), andΔP_(solution) is the pressure drop across the test section for thesolution of water, friction reducer, and biocide. The results are shownin FIG. 6.

In FIG. 6, a control was included where no biocide was injected into thesystem. In samples where biocide was added, the biocide injection pointsare represented by vertical lines at 30 seconds and 150 seconds, whichcorrespond to times of 3:00 minutes and 5:00 minutes after theinitiation of the test. As shown in FIG. 6, the % FR data from 0 to 30seconds represent the friction reduction performance of the pure polymersolution, which increases slightly with time due to continued inversionin the loop.

The introduction of 500 ppm of each respective biocide sample had nonegative effect on the performance of the friction reducer. As shown inFIG. 6, after slight differences in inversion from 30 to 90 seconds, theresults of each experiment appear nearly identical from 90 seconds to120 seconds.

Additional biocide was introduced to bring the total biocide loadinglevel to 1000 ppm. The % FR results for WB Thione did not significantlydeviate from the performance of the control sample during the 150 to 420second time interval. Similarly, the % FR for Glut remained even withthat of the blank sample over the same time interval. These dataindicate that WB Thione and Glut do not have an adverse impact onfriction reducer performance at this dosage range (1000 ppm).

The performance of the friction reducer in the presence of CB Thionedeclines relative to the performance of the blank from 150 to 420seconds. This effect is verified by comparing the % FR data through thelast 10 seconds of the test. These data indicate a % FR of 46.7% for thecontrol sample and 43.5% for the CB Thione, respectively.

However, the introduction of the THPS biocide sample resulted in severeperformance degradation of the friction reducer. After an initial dropin % FR, the friction reduction performance plateaus, then continues todrop with increasing time. The final % FR results were 46.7% for thecontrol sample, and 27.8% for the THPS sample. The results showed thatthe WB Thione and Glut had no effect on the performance of the polymerat the prescribed dosage amount. It was also shown that CB Thione had arelatively minor detrimental effect on polymer performance when dosed at1,000 ppm, causing a 3.2% drop in absolute friction reduction. THPScaused a 19.9% decline in absolute friction reduction at a 1,000 ppmdosage, which eliminated over 40% of the original friction reductioncapacity of the polymer.

Example 6

In this example, the biocidal effectiveness on sulfate reducing bacteria(SRB) and acid producing bacteria (AB) for biocide formulationscontaining CB Thione and WB Thione to Glut and THPS was examined.

A one gallon sample was separated from a five gallon sample of frac pondwater for these studies. The frac pond water sample included SRB and AB.Ten mL of a 10⁹ cfu/mL inoculum of SRB grown in anaerobic API brothcontaining an O₂ scavenger and 10 mL of a 10⁹ cfu/mL inoculum of ABgrown in anaerobic phenol red (anPR) broth containing an O₂ scavengerwere added to the one gallon frac pond water sample, mixed well andallowed to incubate for a period of time sufficient to achieve a desirednumber of SRB and AB. All broth media for inoculum and serial dilutioncounts in this study was made at 4% salinity to match the salinity ofthe original frac pond water measured by total dissolved solids testing.To increase nutrient value and to emulate on-site friction reducingadditives, a 30 weight % acrylic acid, 70% acrylamide copolymer wasadded to the inoculated gallon of frac pond water sample at 300 ppm andthen referred to as the spiked frac pond water sample. The spiked samplewas then divided into 99.0 g aliquots for testing the effect of variousbiocides at various concentrations on the SRB and AB over a 180 daycontact time. One spiked aliquot would serve as the control sample towhich no biocide would be added. Challenges were made to all aliquotsusing 0.5 mL of 10⁸ SRB and 0.5 mL of 10⁸ AB at 14, 28, and 129 dayscontact time.

The biocides included a 20% water based Thione (WB Thione), a 24%caustic based Thione (CB Thione), a 25% Glut, and a 35% THPS. Stockbiocide solutions of various concentrations were made from thesebiocides as described below.

The WB Thione stock solutions were prepared by adding 3.0 g of thebiocide to 17.0 g of sterile distilled water to form an intermediatesolution, followed by combining each intermediate solution with water inthe amounts shown in Table 1 below to make the descending concentrationsas shown in Table 1.

TABLE 1 Stock WB Thione Intermediate Water Total Solution ConcentrationSolution Added Amount Sample (ppm) (g) (g) (g) AA 25000 1.67 8.33 10.00AB 50000 3.33 6.67 10.00 AC 100000 6.67 3.33 10.00 AD 150000 20.00 0.0020.00

The CB Thione stock solutions were prepared by adding 3.0 g of thebiocide to 17.0 g of sterile distilled water to form an intermediatesolution, followed by combining each intermediate solution with water inthe amounts shown in Table 2 below to make the descending concentrationsas shown in Table 2.

TABLE 2 Stock CB Thione Intermediate Water Total Solution ConcentrationSolution Added Amount Sample (ppm) (g) (g) (g) BA 25000 1.67 8.33 10.00BB 50000 3.33 6.67 10.00 BC 100000 6.67 3.33 10.00 BD 150000 20.00 0.0020.00

The Glut stock solutions were prepared by adding 1.0 g biocide to 19.0 gof sterile distilled water to form an intermediate solution, followed bycombining each intermediate solution with water in the amounts shown inTable 3 below to make the descending concentrations as shown in Table 3.

TABLE 3 Stock Glut Intermediate Water Total Solution ConcentrationSolution Added Amount Sample (ppm) (g) (g) (g) CA 5000 1.00 9.00 10.00CB 10000 2.00 8.00 10.00 CC 20000 4.00 6.00 10.00 CD 50000 20.00 0.0020.00

The THPS stock solutions were prepared by adding 1.0 g of the biocide to19.0 g of sterile distilled water to form an intermediate solution,followed by combining each intermediate solution with water in theamounts shown in Table 4 below to make the descending concentrations asshown in Table 4.

TABLE 4 Stock THPS Intermediate Water Total Solution ConcentrationSolution Added Amount Sample (ppm) (g) (g) (g) DA 5000 1.00 9.00 10.00DB 10000 2.00 8.00 10.00 DC 20000 4.00 6.00 10.00 DD 50000 20.00 0.0020.00

Next, 1 g of each biocide stock solution was added to the appropriatelylabeled 99.0 g aliquot. Also, 1.0 g of sterile water was added to thecontrol aliquot. The concentrations of the biocides present in eachaliquot are provided below in Table 5.

TABLE 5 WB Thione CB Thione Glut THPS Control Concentra- Concentra-Concentra- Concentra- (ppm) tion (ppm) tion (ppm) tion (ppm) tion (ppm)0 AA 250 BA 250 CA 50 DA 50 AB 500 BB 500 CB 100 DB 100 AC 1000 BC 1000CC 200 DC 200 AD 1500 BD 1500 CD 500 DD 500

The aliquots were then incubated at room temperature in the dark for theentire study, i.e., 6 months. During the 6 month period, each aliquotwas tested to determine the log quantity of SRB and AB in each aliquotat each of the following contact times: 7 days, 14 days, 21 days, 28days, 35 days, 42 days, 56 days, 90 days, 136 days, and 180 days. Usingsterile syringes, this testing was performed by serial diluting thealiquots into sealed 9.0 mL anaerobic API broth and anaerobic PR brothbottles, both media containing an O₂ scavenger, in the appropriatelabeled set of SRB bottles (6 for each aliquot) and AB bottles (6 foreach aliquot) until a color change occurred, indicating the log quantityof organisms present in each aliquot. The control sample was serialdiluted in 9 media bottles for a possible 10⁹ count. The SRB bottlesthat did not undergo a color change were examined for 21 days, and theAB bottles that did not undergo a color change were examined for 14days. As shown in Tables 6-9 below, at 180 days contact time, thecontrol contained >10⁹ cfu/mL of both types of bacteria, whereas thealiquots treated with WB Thione and CB Thione biocides contained no orlow levels of SRBs or ABs in most cases and maintained that controlthrough three substantial challenges with native organisms. However, thealiquots treated with Glut lost all control of SRB and AB after the2^(nd) challenge on day 28 and the aliquots treated with THPS dependingon treatment concentration, lost all control of SRB and AB from 1 to 21days contact time particularly after the 1^(st) challenge on day 14.Thus, the Thione proved to be much more effective at inhibiting SRB andAB growth in frac water than the Glut and THPS treatments.

Acid producing bacterial counts (AB) in the control increased one logvalue from 10⁸ to >10⁹ over the course of the 180-day study. Twoversions of Thione chemistries were tested against THPS and Glut withexcellent comparable results using the WB Thione and the CB Thione. Bothshort term and especially long term control were exceptional with theThione chemistries in comparison with industry standards of Glut andTHPS. Control was also maintained with all concentrations of the Thionechemistries through three substantial challenges with the exception of250 ppm CB Thione which failed after the third challenge at 129 days ascompared with treatment at all levels of Glut and THPS which failed withearly challenges. In particular, treatment with four levels of THPSfailed after challenging once at 14 days contact time and with allconcentrations of Glut after challenging twice at 14 and 28 days contacttime. All testing stopped when failure to control AB occurred.

Sulfate Reducing bacterial counts (SRB) in the control decreased from10⁹ to 10⁸ over the 180-day course of the study. As above with AB, bothformulations of Thione chemistries provided exceptional control overboth the short and long term for SRB through 3 substantial challenges atall concentrations tested except the 250 ppm treatment of CB Thionewhich lost control after the third challenge on day 129. Comparatively,THPS failed completely after challenging once at 14 days contact time atall concentrations and Glut failed completely at all concentrationsafter challenging twice at 14 and 28 days contact time. All testingstopped when failure to control SRB occurred.

TABLE 6 Log 10 Anaerobic Sulfate Reducing Bacteria/mL* Bioc. Conc. 7 1421 28 35 42 56 90 136 180 in ppm “as is” Days Days Days Days Days DaysDays Days Days Days   0 ppm ≧9 6 14 ≧9 ≧9 28 ≧9 ≧9 ≧9 ≧9 129 ≧9 ≧8(Control) WB Thione DAY DAY DAY  250 ppm 0 1 CHALLENGE 0 0 CHALLENGE 0 00 0 CHALLENGE 1 0 (AA) AT AT AT  500 ppm 0 0 10⁸ 0 0 10⁹ 0 0 0 0 10⁹ 0 0(AB) 1000 ppm 0 0 0 0 0 0 0 0 0 0 (AC) 1500 ppm 0 0 0 0 0 0 0 0 0 0 (AD)CB Thione  250 ppm 1 1 0 0 0 0 0 0 ≧3 ≧3 (BA)  500 ppm 0 0 0 0 0 0 0 0 10 (BB) 1000 ppm 0 0 0 0 0 0 0 0 0 0 (BC) 1500 ppm 0 0 0 0 0 0 0 0 0 0(BD)

TABLE 7 Log 10 Anaerobic Sulfate Reducing Bacteria/mL* Bioc. Conc. 7 1421 28 35 42 56 90 136 180 in ppm “as is” Days Days 14 Days Days 28 DaysDays Days Days Days Days Glut  50 ppm 0 0 DAY 0 0 DAY ≧3 ≧6 ≧6 ≧6DISCONTINUED (CA) CHALLENGE CHALLENGE 100 ppm 0 0 AT 0 0 AT ≧3 ≧6 ≧6 ≧6DISCONTINUED (CB) 10⁸ 10⁹ 200 ppm 0 0 0 0 ≧3 ≧6 ≧6 ≧6 DISCONTINUED (CC)500 ppm 0 0 0 0 ≧3 5 ≧6 ≧6 DISCONTINUED (CD) THPS  50 ppm ≧6 ≧6 ≧6 ≧6 ≧6≧6 ≧6 ≧6 DISCONTINUED (DA) 100 ppm 5 5 ≧6 ≧6 ≧6 ≧6 ≧6 ≧6 DISCONTINUED(DB) 200 ppm 0 0 ≧6 ≧6 ≧6 ≧6 ≧6 ≧6 DISCONTINUED (DC) 500 ppm 0 0 4 3 3≧6 ≧6 ≧6 DISCONTINUED (DD) *Six serial dilution bottles were used foreach treated sample and 9 bottles for the untreated control.

TABLE 8 Log 10 Anaerobic Acid Producing Bacteria/mL* Bioc. Conc. 7 14 2128 35 42 56 90 135 180 in ppm “as is” Days Days Days Days Days Days DaysDays Days Days   0 ppm 8 6 14 ≧9 ≧9 28 ≧9 ≧9 ≧9 ≧9 129 ≧9  ≧9  (Control)WB Thione DAY DAY DAY  250 ppm 2 1 CHALLENGE 1 1 CHALLENGE 1 0 1 0CHALLENGE 2 1 (AA) AT AT AT  500 ppm 1 1 10⁹ 0 0 10⁸ 0 0 0 0 10⁶ 0 0(AB) 1000 ppm 0 0 0 0 0 0 0 0 0 0 (AC) 1500 ppm 0 0 0 0 0 0 0 0 0 0 (AD)CB Thione  250 ppm 1 1 1 1 1 1 1 1 ≧3* ≧3* (BA)  500 ppm 1 1 1 1 1 0 0 01 0 (BB) 1000 ppm 1 0 1 0 1 1 1 0 1 0 (BC) 1500 ppm 0 0 0 1 0 0 0 0 0 0(BD) *Dilutions were made to 10³ only

TABLE 9 Log 10 Anaerobic Acid Producing Bacteria/mL* Bioc. Conc. 7 14 2128 35 42 56 90 136 180 in ppm “as is” Days Days 14 Days Days 28 DaysDays Days Days Days Days Glut  50 ppm 0 0 DAY 1 0 DAY ≧3 ≧6 ≧6 ≧6DISCONTINUED (CA) CHALLENGE CHALLENGE 100 ppm 0 0 AT 0 0 AT ≧3 ≧6 ≧6 ≧6DISCONTINUED (CB) 10⁹ 10⁸ 200 ppm 0 1 0 0 ≧3 ≧6 ≧6 ≧6 DISCONTINUED (CC)500 ppm 0 0 0 0 ≧3 4 ≧6 ≧6 DISCONTINUED (CD) THPS  50 ppm 5 ≧6 ≧6 ≧6 ≧6≧6 ≧6 ≧6 DISCONTINUED (DA) 100 ppm 5 5 ≧6 ≧6 ≧6 ≧6 ≧6 ≧6 DISCONTINUED(DB) 200 ppm 1 0 ≧6 ≧6 ≧6 ≧6 ≧6 ≧6 DISCONTINUED (DC) 500 ppm 0 0 4 3 4 3≧6 ≧6 DISCONTINUED (DD) *Six serial dilution bottles were used for eachtreated sample and 9 bottles for the untreated control.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

1. A method of recovering a production fluid from a subterraneanformation, comprising: displacing a well injection composition through awellbore down to the subterranean formation to force or enhance theproduction fluid from the subterranean formation, the well injectioncomposition comprising an injection fluid and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth.
 2. The method of claim 1, wherein theinjection fluid comprises an aqueous fluid.
 3. The method of claim 1,wherein the injection fluid comprises fresh water or salt water.
 4. Themethod of claim 1, wherein the production fluid is oil and the injectionfluid is at least partially miscible with the oil.
 5. The method ofclaim 1, wherein displacing the well injection composition through thewellbore down to the subterranean formation to force or enhance theproduction fluid from the subterranean formation defines a wellinjection process, a stimulation, a squeeze process, a waterfloodprocess, or a packing process.
 6. A cement composition comprising: acement; and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth.
 7. The cement composition of claim 6, whereinthe cement composition is a squeeze cementing composition.
 8. The cementcomposition of claim 6, further comprising a fluid for making the cementcomposition flowable.
 9. A method of cementing, comprising: injecting acement composition into a permeable zone of a wellbore, the cementcomposition comprising a cement and a biocide comprising3,5-dimethyl-1,3,5-thiadiazinane-2-thione in an amount effective toinhibit bacterial growth; and allowing the cement composition to set.10. The method of claim 9, further comprising providing the cementcomposition in dry form and combining the cement composition with afluid before said injecting.
 11. The method of claim 9, wherein a cementsheath is located in an annulus of the wellbore, and wherein a conduitis located inside the cement sheath.
 12. The method of claim 11, whereinthe permeable zone is in the cement sheath.
 13. The method of claim 11,wherein the permeable zone is in the conduit.
 14. The method of claim11, wherein the permeable zone is between the cement sheath and theconduit.
 15. The method of claim 11, wherein the set cement compositionsubstantially plugs the permeable zone.